Robotic inspection device and mechanical inspection method

Abstract

A robotic device 300 for inspecting wind turbines comprises a generally longitudinal body 302 with legs 316 on opposite sides 312,314 of the body, each comprising articulated limb segments 328,332 and

Description

FIELD This invention relates to robotic devices configured to perform inspections of wind turbines. In particular, the invention relates to robotic devices comprising a plurality of legs that can move across the surfaces of wind turbines and configured to carry out inspections of the surfaces of wind turbines. BACKGROUND Wind turbines require inspection and maintenance to remain efficient and operational. The costs associated with structural and component failures are significant and if these failures are not detected quickly and rectified, damage of critical components can occur. If structural or component failures lead to unscheduled stoppages, there is the additional cost of loss of electricity sales. Wind turbines may be based on land or offshore, for example as part of a floating wind farm for generating electricity. It is predicted that by 2030, floating wind farms will become the norm, with significantly larger turbines generating over 15MW of energy, compared to the 7MW drivetrains today. Offshore turbines operate in harsh and extreme environments such as the North Sea. Traditionally, the inspection and maintenance of wind turbine blades has been reactive. Currently, for wind turbines, systems are in place which use drones with cameras or other detectors to identify damage to the structure. Drones capture the initial inspection image with follow-ups using rope access technicians to look at defects identified in the images. However, the danger to which rope access technicians are exposed is great, and the time taken in undertaking this work and the associated cost is significant. These costs increase further offshore. Delivering repair vessels and supplying heavy inspection and repair machinery to the remote locations of offshore wind turbines is time consuming and costly. Various other solutions for undertaking structure inspection exist. There have been recent attempts to make robots that are able to scale the tower of a wind turbine for the purposes of inspection and maintenance. Similar solutions exist for other large structures. The Applicant’s prior robotic device 300 is disclosed in GB2598756 and shown in Figures 1-3. The robotic device could be used to inspect wind turbine blades during other service downtime. However, the robotic devices currently available may still require human involvement during some types of inspection process. It would be desirable to allow inspections to be carried out using advances in robotics and reduce the need for human intervention. In this way, inspection processes become more automated and efficient, and the limited number of skilled technicians can be utilized more effectively, allowing more wind turbines to be maintained. By providing detailed inspection data as efficiently as possible, forecasting structural failures becomes more feasible, thereby minimizing the frequency of scheduled, and unscheduled, maintenance and downtime of the wind turbine. Therefore, there is a need for improved robotic devices and methods for inspection of wind turbines, which overcomes the problems in the art. SUMMARY Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. The detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended to be given by way of example only. In a first aspect of the invention, there is provided a robotic device for inspecting wind turbines, the robotic device comprising: a body defining a longitudinal axis; a plurality of legs arranged on opposite sides of the body, each leg comprising two or more articulated limb segments and a foot, wherein the legs enable the robot to crawl over a crawling surface of the wind turbine; a chamber for containing a liquid to aid an inspection; a dispensing device attached to the body for applying the liquid to an inspection surface of the wind turbine; a sensor attached to the body for carrying out the inspection; and wherein the legs are configured to allow movement of the body relative to the feet, when the feet are fixed on the crawling surface, to cause the dispensing device to be reversibly brought into contact with the inspection surface and to deposit a volume of the liquid on the inspection surface to allow inspection. This robotic device may be configured to walk on surfaces, such as those of a wind turbine, using a crawling movement and undertake inspections of the surface. The crawling robotic device could significantly increase the efficiency of inspections on wind turbines by reducing the need for human intervention in the inspection process and thereby reducing costs. The robotic device can efficiently provide detailed inspection data in order to forecast structural failures, thereby minimizing the frequency of maintenance and downtime of the wind turbine, and reducing current costs. The robotic device comprises a sensor to carry out inspections on the inspection surface. The sensor may comprise an ultrasonic probe. Ultrasonic testing is a technique for non-destructive testing to assess structural integrity structures and mechanical components. An ultrasonic probe includes a transducer that generates high frequency ultrasonic waves which, after being introduced into a material of the test subject, propagate through the material along a wave path. When there is a flaw or discontinuity, such as a crack, in the wave path, part of the ultrasonic wave is reflected back from the flaw region. The corresponding ultrasonic wave (the reflected wave) is received by the transducer and transformed into an electrical signal representative of the flaw. The ultrasonic probe can scan the surface of a structure to provide an image of the structure, providing details about the internal structure, the surface conditions and any defects. For example, the ultrasonic test may be used for measuring the bolt elongation of wind turbine tower bolts to ensure that they have the required pre-tension. Further, the ultrasonic test may be used to check for defects and damage within the composite laminate material of a wind turbine blade that cannot be seen from a non-contact visual inspection, or the welds of metallic structures such as the welded connections of a wind turbine tower. These techniques are applicable to many other industries such as aviation and shipping. For successful ultrasonic testing, it is important that the surface of the test subject is properly coupled with the transducer. Application of a liquid (also described as a coupling liquid, or couplant) is required to ensure that there is no air gap between the inspection surface and the ultrasonic probe, thereby enabling effective transfer of acoustic waves so the ultrasonic test probe can reliably scan the material below. This liquid couplant is generally necessary because of the high acoustic impedance mismatch between air and the solid surface. The liquid may be water or a more viscous substance. Optionally, the liquid may be a gel. Wind turbines operate in harsh wind and rain environments and many of their surfaces are vertical to the ground. Therefore, the use of a viscous gel couplant rather than water may have the advantage that the couplant remains adhered to the inspection surface during the inspection action. The legs of the robotic device may be configured to allow movement of the body relative to the feet, when the feet are fixed on the crawling surface, so that the sensor is reversibly brought into contact with the inspection surface and the volume of liquid on the inspection surface in order to carry out an inspection. In this way, the robotic device is able to perform the inspection, without the need for human intervention. The legs of the robotic device may be configured so that the movement of the body relative to the feet, when the feet fixed on the crawling surface, is substantially perpendicular to the longitudinal axis. In other words, the robotic device may be configured to perform a squatting action to cause the dispensing device to be brought into contact with the inspection surface and to deposit a volume of the liquid (such as a gel) on the inspection surface to allow inspection. From a standing position, the robotic device may be programmed to simultaneously bend each leg at the lower articulated joint, the upper articulated joint and ankle joint, while the feet remain stationary on the crawling surface, so that the body of the robotic device moves downwards towards the inspection surface. In this case, the inspection surface is the same surface as the crawling surface, or at least in a similar plane as the crawling surface, and the movement of the body relative to the feet is substantially perpendicular to the longitudinal axis. The body of the robotic device moves towards the inspection surface and the dispensing device deposits some liquid on the inspection surface. The robotic device may be programmed to perform the reverse of the squatting action, in order to return to a standing position. In this way, the dispensing device is reversibly brought into contact with the inspection surface. Traditionally, inspections such as ultrasonic inspections are carried out manually, with the operator dispensing the liquid couplant directly onto the surface being inspected. By programming this robotic device to move in a particular way, the robotic device itself can precisely deposit the liquid couplant onto the inspection surface without the need for human intervention. The robotic device is then perfectly positioned to carry out the inspection itself. Also, there is no need for additional equipment on the robotic device to power the dispensing action. Overall, the inspection process becomes more automated and efficient, and the limited number of skilled technicians can be utilized more effectively, allowing more wind turbines to be maintained. By providing detailed inspection data as efficiently as possible, forecasting structural failures becomes more feasible, thereby minimizing the frequency of scheduled, and unscheduled, maintenance and downtime of the wind turbine. The legs of the robotic device may be configured to allow movement of the body relative to the feet, when the feet are fixed on the crawling surface, so that the sensor is reversibly brought into contact with the volume of liquid on the inspection surface in order to carry out an inspection. The reversible squatting action of the robotic device may be repeated to bring the sensor into contact with the inspection surface after the gel has been deposited. The robotic device may be programmed to land the inspection probe on the gel and on the inspection surface. Alternatively, the robotic device may be programmed to dispense the liquid couplant and land the inspection probe on the gel and on the inspection surface in a single squatting action. In this way, the inspection process becomes more efficient and conserves energy for the robotic device. The legs of the robotic device may be configured so that the movement of the body relative to the feet, when the feet are fixed on the crawling surface, is substantially along the longitudinal axis. In other words, the body of the robotic device may be programmed to move forwards and backwards with respect to the legs and / or the feet while the legs are fixed to the crawling surface at their feet. In this way, the robotic device can perform a lurching action to cause the dispensing device to be brought into contact with the inspection surface and to deposit a volume of the gel on the inspection surface to allow inspection. For example, the robotic device may comprise a plurality of carriages, each carriage connecting a leg to the body and being configured to allow each leg to translate in a longitudinal direction relative to the sides of the body. From a standing position and while the feet remain stationary on the crawling surface, the robotic device may be programmed to use the carriages on either side of the body to allow the body to translate in a longitudinal direction relative to the stationary feet. In this case, the inspection surface may be in a different plane to the crawling surface (for example, the inspection surface may be perpendicular to the crawling surface), and the movement of the body relative to the feet is substantially along the longitudinal axis. The body of the robotic device moves towards the inspection surface and the dispensing device deposits some gel on the inspection surface. The robotic device may be programmed to perform the lurching action in reverse in order to return to its original position. In this way, the dispensing device is reversibly brought into contact with the inspection surface. Again, the legs of the robotic device may be configured to allow movement of the body relative to the feet, when the feet are fixed on the crawling surface, so that the sensor is reversibly brought into contact with the volume of liquid on the inspection surface in order to carry out an inspection. The reversible lurching action of the robotic device may be repeated to bring the sensor into contact with the inspection surface after the gel has been deposited. The robotic device may be programmed so that the probe lands directly on the gel on the inspection surface. Alternatively, the robotic device may be programmed to dispense the liquid couplant and land the inspection probe on the gel and on the inspection surface in a single lurching action. In this way, the inspection process becomes more efficient and conserves energy for the robotic device. This robotic device is able to stand on a vertical crawling surface and perform a lurching action towards an inspection surface which may be perpendicular to the crawling surface. For example, the tower bolts on wind turbines needs to be periodically inspected using ultrasonic testing to check that the bolts have the correct pre-tension. The lurching action of the robotic device may be used to inspect the condition of the tower bolts to predict any future maintenance needs. In this case, the crawling surface may be the vertical tower wall of the wind turbine and the inspection surface may be a bolt head which lies perpendicular to the tower wall. By having an efficient automated system to assess the condition of the bolts, without requiring human intervention, the heavy hydraulic equipment needed to tighten the bolts is brought to the wind turbine only when necessary. This in turn saves costs and reduces the need for downtime of the wind turbine. The feet of the robotic device are fixed to the crawling surface during the inspection process. It is to be understood that the number of feet fixed to the crawling surface during the inspection process is the minimum number required to keep the robotic device steady during the inspection process. It is plausible that some feet may not need to be fixed to the crawling surface for the robotic device to successfully carry out an inspection. The liquid dispenser may be a mechanical pump with a nozzle, which dispenses liquid when the nozzle is pushed onto a surface. The nozzle of the liquid dispenser and the probe may be oriented in the direction of the inspection surface. The robotic device may be programmed to use computer vision, machine learning and / or Al so that the liquid dispenser and the probe are oriented substantially perpendicular to the inspecting surface, so that the nozzle can be depressed by the movement of the robotic device and the probe lands directly on the dispensed liquid couplant on the inspecting surface. The shape of the nozzle may be varied (see Figure 4) to produce differently shaped deposits of gel. Different nozzles may be designed that enable the dispensed couplant gel to take different forms, for example, the volume of gel deposited may be disc shaped or substantially spherical. The shape of the deposited gel can be adjusted to match the shape and size of the probe and account for any surface irregularities in the surface being inspected. The dispensing device may be configured to deposit a set volume of liquid suitable for carrying out the inspection. This ensures that liquid is not wasted with only the necessary amount of gel used for each inspection, and ensures the maximum number of inspections can be carried out for a given volume of liquid in the chamber. The robotic device may be programmed to dispense a measured volume of liquid onto the inspection surface. For example, the body of the robotic device may be programmed to move a precise distance towards the inspection surface, and / or the mechanical pump may comprise a dispenser plunger within a lumen and the robotic device programmed to allow the plunger to move a set distance within the lumen to dispense a set volume of liquid. The robotic device may comprise a couplant sensor adapted to indicate a presence of the couplant in a space between the ultrasonic probe and the inspection surface. Therefore, in the event that liquid couplant is not correctly dispensed onto the inspection surface, the dispensing action may be repeated. The chamber for containing the liquid may be mounted on the body of the robotic device. The chamber may be mounted on the body in a position aligned with the longitudinal axis of the body in order to minimise any turning effects on the body through weight or wind loading. Optionally, the chamber is mounted to a lower or underside portion of the robotic device’s body. By mounting the chamber on the robotic device, rather than the liquid couplant being supplied via an umbilical, the robotic device is able to move freely over the surface and into tight spaces of the structure to be inspected without being encumbered by an umbilical tether. Alternatively, the chamber may be connected to the robotic device via an umbilical. Thus, a connection for an umbilical may be provided on the body of the robotic device, the connection comprising contacts or ports for supplying the robotic device with the liquid couplant. The advantage is that size of the chamber is not restricted by the ability of the robotic device to carry the weight of the chamber containing the liquid couplant. The chamber is in fluid connection with the dispensing device to define a flow path for the liquid couplant from the chamber to the dispensing device. The dispensing device and the sensor may be mounted anywhere on the robotic device which enables the dispensing device and sensor to meet with the inspection surface during a squatting action or lurching action. The dispensing device and the sensor may be mounted may be positioned at one end of the body. Optionally, the dispensing device and the sensor may be mounted at either the front end or the rear end of the body. For example, the dispensing device and the sensor may be mounted anywhere on the top side, underside, front, back or left or right sides of the body. Alternatively, the dispensing device and the sensor may be mounted even on the legs. Alternatively, the robotic device may comprise a dispensing device and sensor both at the front end and the rear end of the body. This would have the advantage that less maneuvering of the robotic device may be required to reach particular areas of the inspection surface. The dispensing device and the sensor may be arranged inside a housing to form one unit. The housing provides compactness and means an engineer can change the unit easily and quickly when required (for example, if the ultrasonic probe is to be changed for a different probe). The dispensing device may comprise a tube with a lumen, which defines a flow path for the liquid couplant. The ultrasonic probe may be positioned inside the lumen. This presents a structurally compact design of the device. A distal end of each leg of the robotic device comprises a foot, which may comprise a tool of some form to help the robotic device grip or secure itself to the surface of a structure. The foot of each leg of the robotic device may comprise a suction cup for securing the robotic device to the surface of the wind turbine or other structure. The crawling surface and the inspection surface may be in different planes. The inspection surface may be substantially perpendicular to the crawling surface. For example, the robotic device may be secured to the surface of the wind turbine tower (the crawling surface), and carry out an ultrasonic inspection on a bolt head lying in a plane perpendicular to the surface of the tower (the inspection surface). The position of the dispensing device and the position of the sensor may be adjustable to allow deposition and inspection to be carried out on an inspection surface which is in a plane substantially along the longitudinal axis or substantially perpendicular to the longitudinal axis. The robotic device may be programmed to adjust the position of the dispensing device and the sensor using computer vision, machine learning and / or Al to accurately deposit the couplant on the inspection surface (such as a bolt head) and ensure the probe lands directly on the couplant. The dispensing device and the probe may be mechanically coupled to fix their relative positions. This ensures that direction and position of the ultrasonic wave and the couplant when dispensed remain unaltered with respect to the inspection surface. As mentioned above, the robotic device may be configured to operate on a wind turbine, including wind turbine blades. The robotic device may be configured to walk / crawl along a leading edge of the wind turbine blade to conduct inspection and / or maintenance of the leading edge of the wind turbine blade. For example, the configuration of the legs (which may include its profile and dimensions) should be appropriate for allowing the robotic device to walk / crawl along the leading edge. Moreover, the robotic device may be programmed to recognise automatically the leading edge of the wind turbine blade and then control the movement of its legs autonomously such that it walks / crawls along the leading edge in a tip-wise or rootwise direction to perform the inspection and / or maintenance action. The robotic device may be a multipod (in particular a hexapod) and resemble a robotic creature through comprising a body and a plurality of legs extending from each side. The body may define a longitudinal axis along its length and may comprise a body length. In addition to a front end, a rear end, a left side, and a right side, the body may comprise a top side and an underside to define a substantially box-shaped body where the left side and the right side oppose one another. The left side and the right side may define flat sides of the body. The body of the robotic device may also comprise curved sides and / or rounded front or rear ends and / or a rounded top side or underside, or any combination of these. The robotic device comprises one or more pairs of legs, wherein one leg of a pair of legs is arranged on an opposite side of the body widthways to the other. Such a leg may be moved independently of the leg on the other side of the body. Each leg may comprise two or more articulated limb segments. Articulations may provide a pivot at a hip and a knee of each leg. Each leg may comprise one or more rotational degrees of freedom, and optionally three rotational degrees of freedom. These rotational degrees of freedom may be provided by one or more of the articulations between limb segments. Each leg may also comprise a foot wherein the foot of each leg may also be articulated, e.g., by way of an ankle joint. In this way, the foot may be configured to rest on a surface of the wind turbine blade or other structure in a substantially perpendicular manner to the surface of the structure. With regard to the ability for each carriage to translate in a longitudinal direction relative to the sides of the body, this means that each of the carriages are able to move in a forwards and back direction along the sides of the robotic device. The hip joint of each leg may be provided (at least in part) by one of the carriages such that each hip joint is able to translate along the side of the robotic device. The carriage may be guided through interaction with a guide provided on the body. Each carriage may comprise a sliding interface configured to couple the leg to the guide, the carriage may further comprise an articulation configured to provide part of the hip joint and to join the carriage via the hip joint to an upper limb segment of the leg. The surface, in particular the crawling surface or the inspection surface, may be any surface that the robotic device is configured to reach. In the example of a wind turbine, this may include any external part of the wind turbine and / or any internal surface, including an interior surface of a turbine blade. The surface may comprise two surface regions where the surface regions are generally opposed to each other on opposite sides of a structure, for example, where the robotic device may need to walk straddling the surface regions with one row of feet on one region and the other row of feet on the other region. The crawling surface may be defined as any surface on which the robotic device can walk or is secured, for example when performing a squatting action or lurching action when carrying out an inspection. The crawling surface may be a wind turbine blade or a tower wall of the wind turbine. The inspection surface may be defined as any surface on which the robotic device carries out an inspection, such as an ultrasonic inspection. The inspection surface may the same as the crawling surface. The inspection surface may be a wind turbine blade, a tower wall, or a bolt head of the wind turbine. The limb segments of the robotic device may be articulated in a way that enables the robotic device to straddle over a leading edge of the wind turbine blade with the feet of opposing legs positioned on opposite sides of the leading edge. The robotic device may be configured to automatically walk and adapt to changing surface shapes when moving across the crawling surface in between carrying out inspections. The robotic device may be configured to crawl inside the wind turbine blade to carry out inspections in the confined spaces within the wind turbine blade structure. The robotic device may be battery powered and may not comprise an umbilical. The robotic device may further comprise a battery housed in the body and the battery may be configured to supply primary power to the robotic device. The battery may be rechargeable. This enables the robotic device to be free of any ancillary equipment and to move freely over the surface and into tight spaces of the structure to be inspected without being encumbered by an umbilical tether. Any turning effects on the body through weight or wind loading or transmission of adverse lateral forces on the robotic device due to the presence of an umbilical are avoided. Alternatively, the battery may be used as a backup power supply in the arrangement that the robotic device is receiving power via an umbilical and that power supply is cut. Each foot of the robotic device may be connected to an articulated limb segment of a leg of the robotic device by an ankle joint which allows the foot to twist about an axis of the leg, and / or allows the foot to tilt with respect to the leg, preferably against a restoring bias. The robotic device may comprise apparatus for cleaning the inspection surface prior to carrying out an inspection. Such cleaning would facilitate a rope access technician with their work, minimising their exposure time on the surface of the wind turbine blade. The robotic device may comprise apparatus for repairing damage found on a wind turbine blade or any other composite structure. The robotic device may be free of any ancillary equipment. Alternatively, an umbilical may be used to connect essential items, such as a data connection. The data connection may convey operating instructions to the robotic device as well as conveying inspection data back to a controller for transmission to a remote station where the data can be analysed. The umbilical may also be configured to provide liquid couplant. There may be more than one umbilical. The robotic device may be launched by a person or a small crane from the nacelle of the turbine by placing it on the root of the blade where it can then be manoeuvred to any part of the wind turbine blade to areas of interest or identified via a drone inspection to be damaged. It could also be dropped off onto a structure using a drone. The robotic device may comprise a camera. This may be arranged on a front region of the body, an underside of the body and / or arranged on a leg. The camera may be an inspection camera, for example, a high-resolution camera with the primary function of obtaining data indicative of the condition of the surface of the wind turbine blade prior to carrying out an ultrasonic inspection. In addition to or alternatively, the camera may be a navigation camera, to assist the robotic device in its movements across the surface of the wind turbine blade. In a second aspect of the invention, there is provided a method of inspecting wind turbines, the method comprising the following steps: securing the robotic device according to the first aspect of the invention to the crawling surface; performing a body movement action, in which the body reversibly moves towards the inspection surface, while the feet are fixed on the crawling surface; performing a dispensing action, in which the body movement action causes the dispensing device to be reversibly brought into contact with the inspection surface and causes a volume of the liquid to be deposited on the inspection surface; and performing an inspection action, in which the body movement action causes the sensor to be reversibly brought into contact with the volume of liquid on the inspection surface and an inspection to be carried out to provide information about the inspection surface. Performing an inspection action may further comprise adjusting the position of the dispensing device and the sensor so that liquid deposition and inspection can be carried out on an inspection surface which is in a different plane to the crawling surface. A body movement action may comprise the squatting action, the lurching action or the reverse of these actions, as previously described. The method may further comprise performing a maintenance action based on the information obtained from the inspection action. Securing the robotic device to the crawling surface may comprise generating suction at a point of contact where the robotic device’s feet are in contact with the crawling surface. In a third aspect of the invention, there is provided a system for inspecting a surface of wind turbines, the system comprising: a robotic device according to the first aspect of the invention, and wherein the robotic device is battery powered; and a wireless control device to remotely control the movement and actions of the robotic device. The robotic device may be battery operated and controlled remotely, so that it is free of any ancillary equipment and able to move freely over the surface and into tight spaces of the structure to be inspected without being encumbered by an umbilical tether. Any turning effects on the body through weight or wind loading or transmission of adverse lateral forces on the robotic device due to the presence of an umbilical are avoided. FIGURES Embodiments in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a perspective view of a robotic device straddling a structure such as a leading edge of a wind turbine; Figure 2 shows a side view of a robotic device; Figure 3 shows a perspective view of a robotic device on a flat surface; and Figure 4 shows two different nozzle shapes of the dispensing device. DESCRIPTION The following description refers to the situation where the claimed robotic device is used for inspecting surfaces of a wind turbine. However, the skilled person would be aware that the following disclosure may also be applicable to other structures such as skyscrapers, bridges, nuclear and other cooling towers as well as other structures which have hard-to-reach or dangerous areas for a human worker, or which have areas that are usually considered inaccessible areas for a human worker. Thus, the robotic device described herein relates to any structure that requires inspection. Figure 1 shows a perspective view of an embodiment of the robotic device 300. The robotic device 300 is straddling a leading edge of a wind turbine blade 350. The robotic device 300 has a body 302 which extends in a longitudinal direction. The body has a front end 304, a rear end 306, a top side 308, an underside 310, a left side 312, and a right side 314. The left side 312 and right side 314 are opposite one another. The body 302 may comprise a rectangular box-shape as shown. Each leg 316 may comprise at least an upper articulated joint 326 (hip joint, or coxa), an upper articulated limb 328 (upper limb segment), a lower articulated joint 330 (knee), a lower articulated limb 332 (lower limb segment), an ankle joint 334, and a foot 336. The foot 336 is connected to the lower articulated limb 332 by the ankle joint 334 and the lower articulated limb 332 is connected to the upper articulated limb 328 by the lower articulated joint 330. The upper articulated limb 328 is connected to the carriage 315 by the upper articulated joint 326. The upper articulated joint 326 can also house the motor 320 and linear bearings 324 which couple each leg 316 to the body 302. The foot 336 of each leg 316 comprises a suction device for securing the robotic device 300 to the surface of the wind turbine blade 350. The foot 336 of each leg 316 comprises a suction cup 340. Each of the legs 316 have three rotational degrees of freedom. For the robotic device 300 depicted here, the upper articulated joint 326 (hip joint) may be configured to provide three rotational degrees of freedom to the rest of the leg 316. The lower articulated joint 330 (knee joint) is configured to provide at least one rotational degree of freedom to the lower articulated limb 332 relative to the upper articulated limb 328. Figure 2 shows a side view of the robotic device 300. The left side 312 and the right side 314 are substantially symmetrical in their arrangements. Figure 3 depict the robotic device 300 in a standing configuration for carrying out an inspection of the inspection surface. The foot 336 of each leg 316 is secured to the crawling surface of the wind turbine. In the case in which the inspection surface is the same surface as the crawling surface, or at least in a similar plane as the crawling surface, the robotic device may be programmed to perform a reversible squatting action to cause the dispensing device to be brought into contact with the inspection surface and to deposit a volume of the liquid (such as a gel) on the inspection surface to allow inspection. Each upper articulated joint 326 (hip joint, or coxa), lower articulated joint 330 (knee) and ankle joint 334 is rotated about its axis to cause the legs to simultaneously bend. The dispensing device is positioned at the front end 304 and / or at the rear end 306 and is orientated towards the inspection surface. The resulting movement of the body relative to the feet is substantially perpendicular to the longitudinal axis. In this way, the body of the robotic device moves towards the inspection surface and the dispensing device deposits some liquid on the inspection surface. The robotic device performs this action in reverse to return to its original standing position. In this way, the dispensing device is reversibly brought into contact with the inspection surface. The squatting and standing action of the robotic device is repeated to bring the sensor into contact with the inspection surface after the gel has been deposited. The sensor is positioned at the front end 304 and / or at the rear end 306 and is orientated towards the inspection surface and the robotic device lands the inspection probe on the gel and on the inspection surface. The illustrated robotic device 300 is a hexapod and comprises three carriages 315 mounted to the left side 312 and three carriages 315 mounted to the right side 314. To each carriage 315, a leg is attached. Thus, each leg 316 is connected to the body 302 via a carriage 315 in a way that allows the movement of each leg 316 and carriage 315 to be guided as the carriage 315 translates along a side of the body 302. In the case in which the inspection surface may be in a different plane to the crawling surface (for example, the inspection surface may be perpendicular to the crawling surface), the robotic device may be programmed to perform a reversible lurching action to cause the dispensing device to be brought into contact with the inspection surface and to deposit a volume of the liquid (such as a gel) on the inspection surface to allow inspection. The crawling surface may be vertical with respect to the ground, such as a wind turbine tower surface. The legs remain fixed and each carriage 315 simultaneously translates along the side 312, 314 of the robotic device 300 on which it is mounted in relation to the body. In this way, the body is translated in a longitudinal direction relative to the stationary feet. The dispensing device is positioned at the front end 304 and / or at the rear end 306 and is orientated towards the inspection surface. The resulting movement of the body relative to the feet is along the longitudinal axis. In this way, the body of the robotic device moves towards the inspection surface and the dispensing device deposits some liquid on the inspection surface. The robotic device performs this action in reverse to return to its original position. In this way, the dispensing device is reversibly brought into contact with the inspection surface. The lurching action and the reverse action of the robotic device is repeated to bring the sensor into contact with the inspection surface after the gel has been deposited. The sensor is positioned at the front end 304 and / or at the rear end 306 and is orientated towards the inspection surface and the robotic device lands the inspection probe on the gel and on the inspection surface. The body 302 in Figure 1 further comprises four sensors 338, where two sensors 338 are positioned on the edge where the front end 304 and the top side 308 meet (e.g., at the upper corners of the body 302 looking forward) and two sensors 338 are positioned on the edge where the rear end 306 and the top side 308 meet (e.g., at the other upper corners of the body 302 looking rearwards). These sensors 338 comprise cameras and other sensors, and are configured to provide navigational aid to the robotic device 300. The sensors 338 are also configured to scan the surface of the structure over which the robotic device 300 is moving. The sensors 338 may provide a controller with information to help the placement of the foot 336 of each leg 316. Figure 4 shows two examples of different nozzle shapes of the dispensing device. The shape of the nozzle may be varied to produce differently shaped deposits of gel. Different nozzles may be designed that enable the dispensed couplant gel to take different forms, for example, the volume of gel deposited may be disc shaped or substantially spherical. The shape of the deposited gel can be adjusted to match the shape and size of the probe and account for any surface irregularities in the surface being inspected. Thus, as shown from the above exemplary embodiments, the present invention can also be seen to provide a multi-legged robotic device where the robotic device has been programmed to perform particular actions to carry out inspections itself, without the need for human intervention. The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms such as “lower,” “upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description only and do not require that the apparatus be constructed or operated in a particular orientation unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the exemplified embodiments. Accordingly, the invention expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto. Any reference herein to specific orientations and relative positions, unless otherwise stated, should be interpreted as referring to the robotic device 300 viewed standing on its legs on a horizontal surface. In use, of course, the robotic device 300 is unlikely to be walking, inspecting or maintaining on a horizontal surface and the references should be viewed accordingly; indeed many of the benefits reside in the new robotic device 300 being more able to cope with uneven, highly curved or edge profiles better than previous robotic devices. Also the robotic device 300 is not limited in terms of direction; the front end may be a rear end and the rear end a front end, depending on the task in hand and the direction of travel. The body 302 extends in a longitudinal direction of the robotic device 300 to define a body length. In a configuration where the body 302 comprises a substantially rectangular box-shaped body as shown, the body length is represented by the length of each of the flat, longitudinally extending, left and right sides 312, 314. It should be appreciated that in the above description of exemplary embodiments, various features are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. While some embodiments described herein include some, but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the disclosure, and form different embodiments, as would be understood by the skilled person. For example, in the following claims, any of the claimed embodiments can be used in any combination. Thus, while certain embodiments have been described, it will be appreciated that other and further modifications may be made thereto without departing from the spirit of the disclosure, and it is intended to cover all such modifications, enhancements, and other implementations, which fall within the true spirit and scope of this disclosure. To the maximum extent permitted by law, the scope of this disclosure is to be determined by the broadest permissible interpretation of the following claims and shall not be restricted or limited by the foregoing detailed description. While various implementations of the disclosure have been described, it will be readily apparent to the skilled person that many more implementations are possible within the scope of the disclosure.

Claims

1. A robotic device for inspecting wind turbines, the robotic device comprising:a body defining a longitudinal axis;a plurality of legs arranged on opposite sides of the body, each leg comprising two or more articulated limb segments and a foot, wherein the legs enable the robot to crawl over a crawling surface of the wind turbine;a chamber for containing a liquid to aid an inspection;a dispensing device attached to the body for applying the liquid to an inspection surface of the wind turbine;a sensor attached to the body for carrying out the inspection; andwherein the legs are configured to allow movement of the body relative to the feet, when the feet are fixed on the crawling surface, to cause the dispensing device to be reversibly brought into contact with the inspection surface and to deposit a volume of the liquid on the inspection surface.

2. The robotic device according to claim 1, wherein the sensor comprises an ultrasonic probe.

3. The robotic device according to claim 1 or 2, wherein the liquid is a gel.

4. The robotic device according to any preceding claim, wherein the legs are configured to allow movement of the body relative to the feet, when the feet are fixed on the crawling surface, so that the sensor is reversibly brought into contact with the inspection surface and the volume of liquid on the inspection surface in order to carry out an inspection.

5. The robotic device according to any preceding claim, wherein the legs are configured so that the movement of the body relative to the feet, when the feet are fixed on the crawling surface, is substantially along the longitudinal axis or substantially perpendicular to the longitudinal axis.

6. A robotic device according to any preceding claim comprising a plurality of carriages, each carriage connecting a leg to the body and being configured to allow each leg to translate in the longitudinal direction relative to the sides of the body.

7. The robotic device according to any preceding claim, wherein the dispensing device comprises a mechanical pump with a nozzle.

8. The robotic device according to claim 7, wherein the shape of the nozzle is varied to produce differently shaped deposits of gel.

9. The robotic device according to any preceding claim, wherein the dispensing device is configured to deposit a set volume of liquid suitable for carrying out the inspection.

10. The robotic device according to any preceding claim, wherein the chamber for containing the liquid is mounted on the body.

11. The robotic device according to any preceding claim, wherein the dispensing device and the sensor are mounted at one end of the body.

12. The robotic device according to any preceding claim, wherein the dispensing device and the sensor are arranged inside a housing to form one unit.

13. The robotic device according to any preceding claim, wherein the foot of each leg comprises a suction cup.

14. The robotic device according to any preceding claim, wherein the robotic device is configured so that the crawling surface and the inspection surface may be in different planes.

15. The robotic device according to any preceding claim, wherein the position of the dispensing device and the position of the sensor is adjustable to allow deposition and inspection to be carried out on an inspection surface which is in a plane substantially along the longitudinal axis or substantially perpendicular to the longitudinal axis.

16. The robotic device according to any preceding claim, wherein the robotic device is configured so that the crawling surface may be a wind turbine blade or a tower wall of the wind turbine.

17. The robotic device according to any preceding claim, wherein the inspection surface is a wind turbine blade, a tower wall, or a bolt head of the wind turbine.

18. The robotic device according to any preceding claim, wherein the limb segments are articulated in a way that enables the robotic device to straddle over a leading edge of the wind turbine blade with the feet of opposing legs positioned on opposite sides of the leading edge.

19. A robotic device according to any preceding claim, wherein the robotic device is configured to crawl inside the wind turbine blade to carry out inspections in the confined spaces within the wind turbine blade structure.

20. The robotic device according to any preceding claim, wherein the robotic device is battery powered and does not comprise an umbilical.

21. The robotic device according to any preceding claim, wherein the robotic device further comprises apparatus for cleaning the inspection surface prior to carrying out an inspection.

22. A method of inspecting wind turbines, the method comprising the following steps:securing the robotic device according to claim 1 to the crawling surface;performing a body movement action, in which the body reversibly moves towards the inspection surface, while the feet are fixed on the crawling surface;performing a dispensing action, in which the body movement action causes the dispensing device to be reversibly brought into contact with the inspection surface and causes a volume of the liquid to be deposited on the inspection surface; andperforming an inspection action, in which the body movement action causes the sensor to be reversibly brought into contact with the volume of liquid on the inspection surface and an inspection to be carried out to provide information about the inspection surface.

23. A method according to claim 22, wherein performing an inspection action further comprises adjusting the position of the dispensing device and the sensor so that liquid deposition and inspection can be carried out on an inspection surface which is in a different plane to the crawling surface.

24. A method according to claim 22 or 23, wherein the method further comprises performing a maintenance action based on the information obtained from the inspection action.

25. A system for inspecting a surface of wind turbines, the system comprising:a robotic device according to any one of claims 1 to 21, and wherein the robotic device is battery powered; anda wireless control device to remotely control the movement and actions of the robotic device.

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